1. Field of the Invention
The present invention relates to a new method of joining by a welding process, at least two layers of a thin polyurethane thermoplastic elastomer film having a thickness in the range of 0.5 to 5.0 mils (0.0127 mm to 0.127 mm), without wrinkling, causing pin-holes or holidays and without burning or charring the material. Such welded polymer films are employed to make gloves, including industrial and medical gloves, condoms, organ bags for endoscopic surgical procedures, catheter balloons, and barrier structures to isolate articles, including medical and surgical instruments from environmental contamination, infectious material and the like.
2. Description of Background and Other information
Natural rubber sheet and film, formed by coagulation of natural rubber latex, have long been employed to form barrier and environmental protective products, such as surgical gloves, condoms, and the like.
In the medical and surgical field, there is a substantial need for effective and reliable infection and contaminant-control barrier products, primary among which are surgical gloves. These products must not leak or rupture nor must there be any breach of the barrier material through porosity, permeability or structural weakness. Desirably, such products should provide protection against accidental cuts and needle sticks, and the like. A long shelf life before use is important, as are physical properties such as resistance to tearing, solvents and other environmental exposure. These features should desirably be attained in products which are thin enough to present minimal interference with tactile sensing and mobility.
Industrial gloves and related barrier apparel and clothing and the like have similar requirements.
Condoms are of increasing importance in the prevention of the spread of AIDS viruses, other sexually transmitted diseases, and for effective contraception.
The use of containment for excised tissue and organs in surgical procedures is also of increasing import in the medical field, particularly in the fast growing field of endoscopic examination and surgery. For example, in the removal of a gall bladder, appendix or other organ or tissue suitable to an endoscopic approach.
Catheter balloons are important in procedures such as angioplasty and in the use of in-dwelling catheters, endotracheal tubes and other devices where an inflatable cuff is required.
Barrier containment for implantable devices, such as cardiac pacemakers and the like, and for surgical instruments inserted into the body during surgical procedures is another area of increasing importance. For example, difficult to clean and sterilize instruments such as liposuction cannulae, endoscopic instruments and other lumen containing and complex instruments where cleaning and sterilizing may be unreliable.
These are products which require thin film or sheet materials, and are frequently made of natural rubber or "latex" film and sheet materials.
Latex sheet or film is normally a porous material with a certain amount of permeability. Latex products are often formed through a dipping technique which, as the latex becomes thinner or is stretched, results in an increase in porosity and permeability. Comparable limitations apply to milled sheets formed on rolling or rubber mills. Certain chemicals and molecules, up to the size of AIDS viruses, can permeate latex without causing rupture or displacement, an undesirable characteristic in barrier protection. Latex cannot provide barrier integrity for devices such as surgical gloves and condoms where barrier protection is of prime importance.
Latex also has limited tensile strength and tear resistance and is highly susceptible to cuts and punctures. In addition, the material has a limited shelf life, and will become more fragile and brittle over time.
In today's society, barrier products require maximum protection to prevent the spread of pathogenic organisms as well as the preventing contamination of otherwise clean or sterile materials or devices. Latex products cannot provide this quality of protection because of material faults inherent in the material formed by available techniques.
There is an increasing proportion of the population of potential latex users, particularly workers in the medical and related fields, that are unable to use latex products because of an allergenic reaction that contact with latex products produce in sensitive individuals. Increasing reports are appearing in the medical literature of anaphylactic shock reactions attributed to exposure to latex products, as well as less serious but quite irritating contact dermatitis. As a result of the frequency and severity of such problems, OSHA regulations and guidelines have recently been established requiring employers to provide workers exposed to blood borne pathogens with an adequate hypo-allergenic substitute or other effective alternatives to contact with natural rubber latex products.
In addition, the contact dermatitis that occurs as a result the customary employment of lubricants and powders with latex products can be severe, painful and require treatment.
Synthetic polymer elastomers are finding a greater use in applications traditionally supplied by latex for rubber goods, both in the medical/surgical fields, and in a variety of commercial and industrial applications.
It has been recognized that polyurethane polymers have properties desirable for many of the rubber goods heretofore made of natural rubber, particularly thermoplastic elastomer polyurethanes.
There has been considerable effort in the industry to provide barrier device products of polyurethane materials as a substitute for latex, but until now, no cost effective and fully reliable method to produce such products has been available.
The dipping technique employed for many natural rubber latex products can be employed with polyurethanes, but have not attained all the advantages and benefits desired. For example, dipping processes are expensive, because of the expensive solvents and the attendant environmental and atmospheric pollution and fire and health concerns required to form and deal with dipping solutions of polyurethanes, while the nature of dipping processes does not produce optimal film properties in any event. It is difficult to attain dip molded films which are reliably free of pin holes and porosity. It is also difficult to achieve uniform film thicknesses required of a number of uses.
Some polyurethane products are formed by joining polyurethanes with the use of adhesive bonding or welding techniques. However, most effective adhesives are poorly tolerated or are completely intolerable in many contexts of use, and are time and labor intensive operations, while welding techniques have been limited to joining layers of polyurethane having a thickness of no less than about 5 mils (0.127 mm).
Until the present invention, the welding of thin layers of polyurethane in the range of 0.5 to 5.0 mils (0.0127 to 0.127 mm) resulted in wrinkles, pin holes, discontinuities, holidays and burn or charring defects. The use of thin polyurethane film has been precluded because of the lack of a safe and a reliable welding method that preserved the integrity of the seam formed by the weld while creating a seam that was of high quality acceptable to users.
The joining of polyurethane to form a seam is well known in the art. Methods such as adhesive bonding, electromagnetic bonding, hot plate welding, induction bonding, insert bonding, radio-frequency sealing, spin welding, thermostacking, ultrasonic sealing and vibration welding have all been described in the literature. None of these methods, however, provide a secure, reliable and reproducible seam where the polyurethane is in the form of a film with a thickness in the range of 0.5 to 5.0 mils (0.0127 to 0.127 mm) and, therefore, are not applicable to polyurethanes less than 5 mils (0.127 mm) in thickness. As those of ordinary skill in the art will recognize, these are the very dimensions of greatest interest fin a very substantial proportion of uses and products.
Generally, the welding of thin polyurethanes, due to the thinness and broad melting point temperature of the material, resulted in several problems, including:
1) film wrinkling during welding;
2) seam pin holes or holidays;
3) too broad of a seam;
4) arcing, charring and burn marks of the polyurethane;
5) risk to the manufacturing operator; and
6) unacceptable levels of failure in use.
There are several problems with current joining, bonding or welding methods in their application to thin polyurethanes. For example, with conventional heat sealing equipment, it is difficult to control temperature accuracy due to a temperature rise with a longer time use. Because of this lack of temperature uniformity critical in thin film joining, wrinkling, pin holes or holidays can occur in the seam.
Electromagnetic bonding for thermoplastic substrata is based on the principle of induction heating: a composition consisting of ferromagnetic particles dispersed in a polymer matrix develops heat when subjected to a high-frequency alternating current source. When this composition is placed between two synthetic polymer elastomers, the heat developed is used to rapidly fuse the abutting surfaces. The technique is limited to thick structures, greater than 5 mils in thickness. In many contexts, the presence of ferromagnetic particles is unacceptable.
Impulse heating creates an unacceptably broad seal. When the material to be sealed is thin, pin holes and holidays result due to uneven and poor temperature control. A sufficient seal cannot be assured and reproducibility is poor.
Radio-frequency welding is also known as R.F. heat sealing, high-frequency sealing, or dielectric heat sealing. A radio-frequency welder directs a large: amount of radio frequency energy into the seam area. The energy causes the molecules of the material to oscillate or vibrate, creating heat. A combination of this heat, and pressure exerted by the pressure component of the welder, causes the materials to fusion bond. The ability and ease at which materials bond is related to their dielectric properties. Radio-frequency bonding works well when the thickness of a thermoplastic polyurethane elastomer film is greater than 5.0 mils (0.127 mm) although the energy intensity required is rather high. In thin film applications, sparking occurs due to arcing which can cause burns and chars to the film. This can also be hazardous to the operator. Radio-frequency welding is not widely employed with thermoplastic polyurethane elastomers because of these limitations.
The most commonly used application of radio-frequency welding is in polyvinyl chloride bonding and embossing in which the melting of the material brought about by molecular vibration. Molecules within the material are subject to periodic stresses caused by a radio frequency field alternating in polarity several million times per second, most often at 27.12 MHz. The amount of heat developed in the material is directly proportional to the amount of radio-frequency power applied to it. If the material has a high dissipation factor, that enables a rise in temperature in a radio-frequency field, when the heat exceeds the melting point of the material under pressure, and such a melt, under control, can be employed to form a fusion bonded joint or weld.
Until now, it has not been possible to convert, particularly for surgical and medical use, the excellent properties of thin thermoplastic polyurethane elastomer materials with a thickness of less than 5 mils (0.127 mm) into effective rubber goods. While polyurethane has been available for many years, the ability to produce thin polyurethane safe and usable barrier products having acceptable seam integrity has not been available. Polyurethanes have properties superior to latex, including structural strength, elasticity and the absence of porosity and permeability.
U.S. Pat. No. 4,463,156 to McGary, Jr. et al., "Polyurethane Elastomer and an Improved Hypoallergenic Polyurethane Flexible Glove Prepared Therefrom", discloses a soft, low modulus, non-crystalline segmented polyurethane glove comprised of specific chemical and physical characteristics that result in a more comfortable and easier to use surgical glove. McGary, Jr. et al. do not suggest or teach a method of joining two layers of thin polyurethane film to form a weld seam through the process of radio-frequency welding in glove fabrication.
U.S. Pat. No. 3,148,235, "Method of Making Plastic Gloves", and U.S. Pat. No. 3,197,786, "Plastic Gloves" to Velonis, disclose a method for making a seamless plastic glove and the glove itself, formed from a film of a fused polyvinyl chloride resin by utilizing dipping forms made from aluminum. The method and product of Velonis does not suggest or teach a method of joining two layers of thin polyurethane film to form a weld seam through radio-frequency welding in glove fabrication.
U.S. Pat. No. 4,684,490 to Taller et al. "Process for Preparation of Polyurethane Condoms", discloses a polyurethane condom formed through a dipping method in which the polyurethane is in the form of an organic solvent solution. The process of Taller et al. does not anticipate or teach a method of joining two layers of thin polyurethane film to form a weld seam through radio-frequency welding in condom fabrication.
U.S. Pat. No. 3,553,308 to Kobayashi et al., "Method for Preparing Polyurethane Molded Articles", is a method in which articles, particularly condoms, are prepared by alternately dipping a condom mold, at a controlled speed, in a polyurethane prepolymer solution and then curing the solution. Kobayashi et al. do not teach or suggest a method of joining two layers of thin polyurethane film to form a weld seam through radio-frequency welding in fabricating a condom.
U.S. Pat. No. 4,576,156 to Dyck et al., "Prophylactic Device and Method", discloses a method of preparing a condom in which a thermoplastic polyurethane elastomer material is deformed using a preformed mandrill in which a vacuum is applied to the system during the deformation step. Dyck et al. does not teach or suggest a method of joining two layers of thin polyurethane film to form a weld seam through radio-frequency welding in producing a condom.
U.S. Pat. No. 3,094,704 to Abildgaard, "Plastic Glove", discloses a seamless plastic glove made from a skin-fitting form-mold plastic layer is produced from an elastomer by spraying a molten or dissolved plastic material on a plurality of molds or forms. Abildgaard does not teach or suggest a method of joining two layers of thin polyurethane film to form a weld seam through radio-frequency welding in the production of gloves.
As has been noted, seam integrity is an essential and critical parameter for barrier devices in preventing the transmission of microscopic particles or for special sensor devices to prevent electrolyte transmission prematurely.